The present invention is directed to a nano-composite comprising a clay and a cationic mediator, wherein the cationic mediator comprises a hydrophobic unit and a cationic unit. The invention is further directed to a composition comprising the nano-composite and a polymer. The composition is useful in preparing products such as tires with improved and well-balanced properties including gas impermeability, cure rates, and superior mechanical characteristics, etc.
In manufacturing rubber products such as a tire, one needs to consider a wide range of factors and various balances between them, such as gas permeability, curing properties such as curing time and curing capability, traction characteristics on dry and wet surfaces, rolling resistance, tread-wear resistance, ring tensile, vulcanization plateau, Shore A hardness, rubber damping properties, elongation, strain, specific gravity, reliability, manufacturability, and cost effectiveness, among others. For example, gas impermeability is important for many rubber products where unsaturated bonds can be attacked by atmospheric ozone. These attacks may, over time, lead to oxidative degradation, which may subsequently lead to chain cleavage. As such, there exists a continuous interest in lowering gas permeability of polymers.
Since the discovery of exfoliated nylon/clay nano-composites by Usuki et al. (J. Mater. Res. 1993, 8, 1174), people have made extensive efforts to lower gas permeability by using well-exfoliated layered materials. A common morphology for miscible polymer-layered material dispersions is known as intercalation and exfoliation, which improves polymeric properties such as mechanical, gas barrier/permeability, thermal, and heat distortion temperature. However, for polymers, particularly nonpolar polymers, well-exfoliated polymer-layered material nano-composites are notoriously difficult to obtain. For example, Wang et. al in the Journal of Applied Polymer Science, Vol. 78, 1879-1883 (2000) describe a process of making clay-rubber mixtures by mixing a styrene-vinylpyridine-butadiene latex with a hydrophilic unmodified clay. The expansion of clay gallery was reported to increase only from 1.24 to 1.46 nm. The limited extent of intercalation is not expected to provide substantial property enhancement in rubber materials.
Although organic ammonium salts have shown improved capability in clay exfoliation, they typically have a low decomposition temperature. As an undesirable effect, organo-clays treated by the ammonium salts may damage or retard the cure process of the rubbery material, especially when free radical cure, sulfur cure, or ZnO cure is employed.
Advantageously, the present invention provides nano-composites that are useful in formulating compositions such as rubbers and tire products with improved and well-balanced properties including gas permeability, thermal stability, cure properties, and/or mechanical properties etc.